In recent years, display devices such as cathode ray tubes (CRTs), liquid crystal displays (LCDs), plasma displays (PDPs), organic/inorganic EL displays, field emission displays (FEDs) are used as display devices in various electronics devices.
On the front face of such a display device, an optical filter is disposed for making display colors vivid by removing unnecessary emission components. For example, the plasma displays are those wherein a mixed gas of xenon and neon is excited by discharge to emit a vacuum ultraviolet light, and the emission of lights from red, blue and green fluorescence substances excited by the vacuum ultra violet light is utilized to obtain the three primary colors emission. In these plasma displays, neon atoms are excited and, upon returning to the ground state, emit a neon orange light around 590 nm (also referred to hereinafter as Ne light); therefore, there is a disadvantage that its orange color is mixed with a red color thus failing to achieve a vivid red color. On the other hand, when xenon atoms are excited and then return to the ground state, a near-infrared light in the vicinity of 800 to 1100 nm (also referred to hereinafter as NIR) is generated in addition to ultra violet light, and the generated near-infrared light causes peripheral devices to malfunction. In a plasma display, therefore, a filter having a function of absorbing and eliminating neon orange light and near-infrared light, for example, a filter that locally reduces the transmittance of a neon orange light and near-infrared light, is disposed on the front face of the display. The filter may also be endowed with a function of correcting the color balance of an image or of improving color purity by regulating transmittance in the visible light wavelength region. A filter for realizing a variety of these filter functions, particularly a NIR absorption filter, has a problem that a dye contained therein is easily deteriorated with ultra violet light (also referred to hereinafter as UV) derived from sunlight etc. For solving this problem, a UV absorption function is also required in some cases.
With advanced functions and widespread use of electric/electronics devices, electromagnetic interference (EMI) is increased, and electromagnetic waves are generated even from the above-mentioned display devices such as PDPs. Accordingly, an electromagnetic wave shielding sheet (electromagnetic wave shielding filter) having an electromagnetic wave shielding function is usually disposed on the front face of PDP or the like. The performance of shielding electromagnetic waves generated from the front face of PDP requires a capability of 30 dB or more in 30 MHz to 1 GHz. In this specification, the term “electromagnetic wave” is used to mean electromagnetic waves not higher than a frequency band in the range of MHz to GHz and is used in distinction from infrared light, visible light and ultra violet light.
The electromagnetic wave shielding sheet used in such application requires not only electromagnetic wave shielding performance but also light permeability. The known electromagnetic wave shielding sheet is, therefore, an electroconductive mesh layer obtained by etching a metallic foil (e.g., a copper foil) attached via an adhesive to a transparent substrate film consisting of a resin film.
As the front filter disposed on the front face of a display, a composite filter in which a NIR absorption function, a Ne light absorption function, a color correction function and a UV absorption function are unified together with an electromagnetic wave shielding function is often used.
For example, Patent Documents 1 and 2 have proposed a composite filter comprising an electroconductive mesh layer and an adhesive layer for attachment of a display, formed in this order on one side of a transparent substrate film, and a NIR absorption filter film and the like laminated on the other side of the transparent substrate film.
Patent Document 3 has proposed a composite filter produced by laminating a metallic foil via an adhesive layer on one side of a transparent substrate film, etching the metallic foil for use as an electroconductive mesh layer, and adding a NIR absorption dye to an adhesive layer for attachment to a display, or adding, to the backside thereof, a resin layer to which a NIR absorption dye was added.
Patent Document 4 describes an acrylic block copolymer composition characterized by: (i) comprising a block copolymer (I) having, in its molecule, at least a triblock structure wherein one polymer block (A1) based on acrylic ester units, and two polymer blocks (B1) different in structure from the polymer block (A1) and based on (meth)acrylic ester units, are bound to one another, or a triblock structure wherein two polymer blocks (A1) comprising acrylic ester units, and one polymer block (B1) different in structure from the polymer block (A1) and based on (meth)acrylic ester units, are bound to one another, the block copolymer (I) having a weight average molecular weight of 120,000 or more and a molecular weight distribution (Mw/Mn) of less than 1.5; and a diblock copolymer (II) wherein one polymer block (A2) based on acrylic ester units, and one polymer block (B2) different in structure from the polymer block (A2) and based on (meth)acrylic ester units, are bound to each other, the diblock copolymer (II) having a molecular weight distribution (Mw/Mn) of less than 1.5; (ii) the ratio of the block copolymer (I):the diblock copolymer (II) contained being 100:50 to 100:500 by mass, and it is described therein that this acrylic block copolymer composition is useful an adhesive composition. However, Patent Document 4 does not describe use of the composition in a display device, endowment thereof with optical filter functions, deterioration of a light absorbing agent therein, or impact resistance thereof at all.
[Patent Document 1] Japanese Patent Application Laid-Open (JP-A) No. 2001-210988
[Patent Document 2] JP-A No. 11-126024
[Patent Document 3] Japanese Patent No. 3473310
[Patent Document 4] JP-A No. 2005-307063
[Patent Document 5] JP-A No. 2002-260539